1. Field of the Invention
This invention pertains to laser mirrors and to high energy laser mirrors in particular. In even finer detail, it relates to liquid mirrors suitable for high energy lasers.
2. Description of Prior Art
Lasers are common light sources in the present world. The growth of laser uses has increased the interest in high energy lasers. One of the limiting factors in the development of high energy lasers, such as CO.sub.2 lasers, has been surface damage and/or deformation of laser mirrors.
Numerous attempts have been made in the prior art to provide cooling of the mirror surface to avoid the heat buildups which damages and/or deforms the surface. Recent attempts to solve this problem include U.S. Pat. Nos. 3,942,880 to Zeiders, 3,932,029 to Weiss and 3,909,118 to Schmidt. These patents rely on a coolant pumped along the back surface of the mirror to absorb heat. The heat transfer flow in such device is not able to prevent heat buildup which produces thermal induced distortions. These devices are also limited by surface damage, e.g., melting or pitting due to hot spots on the mirror surface caused by the mirror's inability to dissipate the energy absorbed from the laser beam.
U.S. Pat. No. 3,371,287 to Haddad uses a liquid reflecting surface. The Haddad patent permits continuous replacement of a surface that is damaged by heating effects. Even the Haddad patent is limited when used in modern high energy lasers. Current lasers produce such high power that Haddad's invention is subject to catastrophic failure due to the low reflectivity of the mirror and the heat buildup of the system as a whole. Static heat buildup in the Haddad mirror causes thermal distortions due to expansion of the various components.
The use of dielectric layers to enhance reflection has been described in "Low-Loss Multilayer Dielectric Mirrors" by D. L. Perry, Applied Optics, Vol. 4, #8, 1965 and in "Computer Design and Fabrication Techniques for a Wideband Dielectric Mirror", by J. Berthold in Applied Optics, Vol. 8, #9, 1969. Further background can be found in "Monographs on Applied Optics No. 4, Metal-Dielectric Multilayers" by John Macdonald, American Elsevier Pub. Co., 1971, and "Optical Properties of Dielectric Films" edited by Norman Axelrod, The Electrochemical Society, 1968.